The present invention relates generally to improvements in a fluid-filled bushing structure for vibration damping or isolation, and more particularly to such a fluid-filled bushing structure which has means for protecting a resilient member against excessive deformation of strain and which is excellent in durability.
In the art of a suspension system for use, for example, on an automotive vehicle, various types of suspension members in the form of arms, rods, links, etc., are connected to the vehicle chassis to suspend a differential gear, wheels, and similar parts of the vehicle so that the suspension members are pivotable in various directions. To damp or absorb vibrations, suspension dampers or isolators in the form of bushings have been commonly used as pivotal connections at both ends of each suspension member. It is also known to use similar bushings as engine mounts which are interposed between an engine and the vehicle chassis to restrain transmission of vibrations from the engine.
Generally, a bushing structure serving as a vibration damper or shock absorber like such suspension bushing or engine mount as stated above, comprises an inner metal sleeve through which is inserted a suitable fulcrum shaft for suspension purpose of the vehicle, an outer metal sleeve disposed concentrically with the inner metal sleeve, and an annular resilient or elastomeric member radially compressed between the inner and outer metal sleeves for damping vibrations through deformation or compression thereof. In recent years, however, it has been proposed to employ a compound bushing structure, i.e., a fluid-filled bushing which is capable of effecting a required vibration damping without having to use a rubber or resilient material of particularly high damping coefficient for the resilient member.
More specifically described, a resilient member interposed between the inner and outer metal sleeves of such a compound bushing as stated above has a plurality of recesses which cooperate with the inner wall surface of the outer metal sleeve to form pockets or fluid chambers which are filled with a suitable incompressible fluid and arranged to be in fluid communication with each other through an orifice. The fluid flows through the orifice from one of the fluid chambers to another upon transmission of vibrations to the bushing, and thus the orifice provides a resistance to the fluid flow which gives a good damping effect.
While such compound bushing structure known in the art is able to provide a desired fluid damping force by means of a resistance (viscosity resistance) to the fluid flow through the orifice, no provisions are made for prevention of an excessive displacement between the inner and outer cylindrical members (sleeves) relative to each other. More particularly, no means are provided for protection against excessive deformation or deflection of the resilient member or rubber insert interposed between the inner and outer sleeves. Under these conditions, the resilient member is deformed according to the magnitude of a load applied thereto. Upon application of an extremely high load, the resilient member may have an excessive deformation (strain), and tends to be damaged due to repetitive deformation thereof in such excessive degree. Thus, the prior art compound bushing structure suffers a problem of low durability or short life.